1. Field of the Invention
This invention relates to hair-dyeing preparations containing substantive hair dyes.
2. Statement of Related Art
Hair-dyeing preparations of the type in question contain substantive hair dyes in a cosmetic carrier. In many cases, such hair-dyeing preparations additionally contain oxidation dye precursors to produce certain shades. The cosmetic carriers used for the substantive hair dyes and oxidation dye precursors, if any, are creams, emulsions, gels, shampoos, foam aerosols or other preparations suitable for application to the hair.
In addition to the oxidation dyes, which are formed by the oxidative coupling of one or more developer components with one another or with one or more coupler components, substantive hair dyes play a prominent part in the dyeing of hair. Substantive dyes have the advantage of being used without the addition of oxidizing agents. The substantive dyes used are predominantly nitrobenzene derivative compounds. They are used either on their own or in combination with other substantive dyes, such as anthraquinone dyes, indophenols, triphenylmethane dyes, cationic azo dyes, or with oxidation dyes.
Good hair-dyeing preparations have to form the required shades with sufficient intensity. They must be readily absorbed by human hair without excessively staining the scalp. The dye finishes produced by them must show high stability to light, heat, perspiration, shampoos and the chemicals used in the permanent waving of hair. Finally, they should be safe to use from the toxicological and dermatological viewpoint.
Among the substantive nitrobenzene derivatives, the nitroanilines and derivatives thereof play an important part because some of these dyes produce intensive, light-stable dye finishes. However, the known substantive nitroaniline dyes have disadvantages in that, on the one hand, they show only limited solubility in water, which leads to problems during formulation of the hair-dyeing preparations, and on the other hand they are not sufficiently fast to washing, i.e. the dye finishes fade considerably after repeated washing. In addition, substantive dyes are required to show high compatibility with other dyes, for example with oxidation dye precursors and with the components normally used in oxidation hair-dyeing preparations because substantive dyes and oxidation dyes are often combined with one another for color modification. Accordingly, high stability to reducing agents and oxidizing agents is necessary.